The performance capability of the restraint systems in vehicles will sharply increase in the future in order to further improve the protection of vehicle occupants. That means that the number of restraint devices and their accompanying triggering devices in the vehicle will drastically increase. Among these restraining devices are, for example, multi-stage-activation air bags for driver and front-seat passenger, knee bags for driver and front-seat passenger, side air bags for driver, front seat passenger and backseat passengers, whereby side air bags can be provided for the head as well as the thoracic region, seat belt tighteners, which can also be activated in multiple stages, possibly also a rollbar, etc. Thus, a complex protection system that includes a plurality of restraining devices is installed for each vehicle occupant. A complex restraint system is described in the German Published Patent Application 1 961 293 and in the Conference Proceedings of the SAE International Congress & Exposition, 2/24-2711997, Detroit, in the article "Bussystem zur Vernetzung von Aktuatoren fur Ruckhaltesysteme" (Bus System For The Connection Of Actuators For Restraint Systems) by J. Bauer, G. Mehler and W. Nitschke. By introducing a bus system that connects all restraining devices to each other, voluminous wiring harnesses can be spared. Provided in this system for each restraining device is a data processing unit, which has essentially a computing unit, data input and output circuits, a memory unit, a time and clock base and a power supply. Also characterized as a peripheral intelligent activation end stage, this data processing unit is arranged in the direct vicinity of the triggering devices belonging to the particular restraint unit, namely in a squib insert or a substrate of the squib itself.
A central control unit connected to the bus line uses a plurality of control signals--e.g. of acceleration sensors, pre-crash sensors and seat occupancy sensors--to determine which of the restraint devices present are to be triggered. If these sensors signal a crash, then the central control unit sends a triggering command through the bus line to all or selected data processing units. Here, the central control unit uses a protocol transmitted through the bus line to address those data processing units for which the triggering command is determined. Also diagnostic commands are output from the central control unit through the bus line to the individual data processing units, which, in turn, send their diagnostic responses back to the central control unit through the bus. The transmitted data are assigned to two different categories. Triggering signals belong to the signal category with highest priority here, i.e. triggering signals require a very high transmission security and have a very high time-related urgency. By contrast, diagnostic queries and diagnostic responses belong to a signal category with lower priority because these do not require a very high transmission security or a very high time-related urgency. According to the related art mentioned here, to distinguish between signals of differing priority, signals with higher priority and higher time-related urgency (triggering signals) are transmitted with a high signal level and a high bit rate and signals with lower priority and lower time-related urgency (diagnostic queries, diagnostic responses) are transmitted with a lower signal level and a lower bit rate. With this type of signal configuration, it is possible to provide two different signal channels that can be separated from one another with a high degree of reliability.
The underlying object of the present invention is to specify a method with which more than two signal channels that are clearly separable from each other can be realized.